The objective of the C-SiG Optical Microscopy Core, is to be a state-of-the-art, user-friendly service that connects investigators with the many optical technologies and applications at a reasonable cost. Under the direction of Dr. Mark McNiven, a well-established cell biologist, the Core integrates existing resources from the Mayo Microscopy and Cell Analysis Core and from individual investigators in the Division of Gastroenterology and Hepatology (GIH) as well as providing additional new technologies not previously available. The Specific Aims of this core are three-fold. First, to provide reliable, accessible, state-of-the-art microscopic technology to all C-SiG members that will facilitate their study of Gl cellular signaling cascades. Second, to educate and train C-SiG members; in the use of both basic and sophisticated cellular imaging methods. Emphasis is placed on providing technical instruction as well as educating faculty on how such approaches can expand the scope and breadth of their scientific programs. Third, to develop and apply state-of-the-art optical imaging technologies, including fluorescent probes and biosensors, to study Gl tissues and/or cells. The most popular Core service is access to the well-maintained C-SiG Confocal Microscopes. The Core also provides instruction, technical advice, data interpretation, and development of novel, innovative optical approaches to the study of signaling pathways in Gl cells and tissues. These services cover a wide range of topics including: real-time computer/video imaging of live cells; confocal microscopy coupled with computer-based 3-D image reconstruction; Fluorescence Resonance Energy Transfer (FRET) applications to measure dynamic protein-protein interactions; Fluorescence Recovery After Photobleaching (FRAP) that allows the quantitation of protein recruitment/turnover; Fluorescence Loss in Photobleaching (FLIP); microinjection of living cells; expression and use of fluorescence-based bioprobes that facilitates the study and localization of specific signaling molecules including both proteins and lipids; the development and application of specific photo-activatable caged-compounds that allow a precise temporal and spatial activation of desired signaling molecules in live cells; Total internal reflection (TIRF) microscopy; multiphoton microscopy, and super-resolution microscopy. Core services have been used by 58% of CSiG members and supported 106 publications.